The coders added some special tags for the Aztec civ. For example, note the "Arrow Knight" entry in the damage bonus section for the Organ gun:

<DamageBonus type ='AbstractArtillery'>0.500000</DamageBonus>

<DamageArea>2.000000</DamageArea>

<DamageBonus type ='AbstractCavalry'>0.500000</DamageBonus>

<DamageBonus type ='Building'>0.750000</DamageBonus>

<DamageBonus type ='Ship'>0.500000</DamageBonus>

<DamageBonus type ='AbstractLightInfantry'>0.500000</DamageBonus>

<DamageBonus type ='xpArrowKnight'>0.500000

The reason for this is that Arrow Knights are essentially the Aztec culverin/mortar combo unit and the Organ Gun has a negative multiplier versus other artillery.

Also, note that the Organ gun doesn't per se have an infantry multiplier like the Horse Artillery does.

One think I like about Organ Guns is that they set up better than Horse Artillery, which often twist and turn trying to place themselves into a formation until some culverin notices and kills them before they even get set up.

Siege eles appear to have a very fast setup time, like light cannons do. I don't know any statistics about this but I've noticed siege eles pretty much don't have a limber mode. They just seem to move at one speed all times. I have actually found this very useful while trying to culv war with someone. You can easily run them away which will cause their culv to pack up, and most of the time you can run back and shoot before they have setup again. Of course this wouldn't work with LC to well, but LC seem to walk at one speed whether in limber mode or not.